With the development, beginning around 1996, of light-emitting diodes (LEDs) capable of emitting white light, LEDs have come into use in flashlights, and in portable headlights for use in activities such as diving, cave exploration, hiking, camping, etc. Moreover, in recent years, with the development of more powerful LEDs, these devices have even displaced incandescent bulbs in some flashlights and personal headlamps. For illumination comparable to that of an incandescent flashlight or personal headlamp, manufacturers have incorporated multiple LEDs into a single lamp. In some cases, for maximum light output, all the LEDs can be operated together. Where maximum light output is not needed, groups of fewer than all of the LEDs in a multiple LED lamp can be selectively operated by suitable switching, in order to avoid excessive battery drain. A similar result can be achieved by electronically adjusting the duty cycle of an LED or group of LEDs.
Although LEDs are generally more efficient than incandescent bulbs insofar as the ratio of light output to electrical power input is concerned, the higher power LEDs still generate a substantial amount of heat, and can fail if they become too hot. Heretofore, it has been difficult to dissipate heat adequately in a high power LED light, especially where plural LEDs are arranged in close proximity to one another. Accordingly, it has been necessary to limit LED power input, or to operate the LEDs intermittently when utilizing maximum power.